Hydraulic systems are often used to control the pressure and flow of pressurized fluid to and from one or more actuators to affect movement of the actuators and implements of a machine to perform tasks. Such hydraulic systems typically include a source of pressurized fluid, a fluid reservoir, and one or more valves selectively communicating one or more chambers of the actuators with the source of pressurized fluid and the fluid reservoir. The source of pressurized fluid is often a variable displacement pump that typically has a minimum displacement necessary to maintain pump lubrication. When the pump operates at the minimum displacement, pressurized fluid is provided downstream of the pump at a predetermined and substantially constant pressure, conventionally referred to as standby pressure. The response time of the hydraulic system, e.g., the time necessary to increase pump displacement and direct pressurized fluid to one or more actuators from standby, is a function of the standby pressure. Control and regulation of the standby pressure to reduce energy loss and increase response time may improve the operation of hydraulic systems.
U.S. Pat. No. 5,680,760 to Lunzman (“the '760 patent) discloses a hydraulic drive system including a pump for delivering fluid under pressure from a reservoir to a plurality of hydraulic actuators via a plurality of closed center type valves. The '760 patent also includes a bypass valve downstream of the pump and configured to selectively communicate fluid from the pump to the reservoir. Specifically, the bypass valve of the '760 patent is fully open when there is little or no usage by the actuators and is moved toward a closed position when one of the plurality of actuators is actuated by one of the plurality of the close center valves. Movement of the bypass valve toward the closed position increases pressure in a supply line interconnecting the pump and the plurality of closed center valves and provides operation of the plurality of closed center valves as if they were open center valves.
Although the bypass valve of the '760 patent may control the pressure of fluid directed from the pump, pressure spikes generated within the system may be communicated to the plurality of closed center valves.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above.